Explanation:
b+g = 297 - eqn1
let the number of boys be b and the number of girls be g
(4/9)*b = (7/9)*g
cross multiply
4x9b = 7x9g
36b=63g - eqn2
from eqn 2
36b = 63g
we can divide both sides by 36 to make b the subject of formula
b=7/4 g
substitute b in eqn 1
b+g=297
7/4 g + g = 297
11/4 g = 297
11g = 297*4
11g=1188
g = 1188/11 = 108
since b+g=297
b+108=297
b=297-108=189
therefore the no of girls is 108 and of boys is 189
189-108 = 81 so there are 81 more boys than the girls